1. Smart Meter Networks
Smart meters monitor the use of utilities, e.g., electricity, heat, gas and water, by a consumer. Typically, the smart meter communicates with a utility provider via network or grid, which can include, perhaps, millions of smart meters. Smart meters can turn utilities on or off, record usage information, detect service outages, unauthorized use, control utility consumption, and manage payments.
Smart meters must reliably and securely communicate with utility providers. Wired or wireless mesh network can be used. A number of protocols are known, e.g., ANSI C12.18, ANSI C12.19, and ANSI C12.21 for optical communications, as well as IEEE 802.15.4, IEEE P1901.2, and 802.11. The European Union uses IEC 61107 and IEC 62056. in Japan, the Energy Conservation is involved in promoting smart metering, as well as public and private utilities.
Smart meters can be connected to utility providers via one or more concentrators. The concentrators receive metering information from the smart meters, and forward the information to the providers for controlling or monitoring the utilities. The concentrator can also broadcast control packets to smart meters for management purposes.
Smart meters can be equipped with lower power and lossy transceivers, such as ZigBee radios, and are deployed in a relatively large geometric region, e.g., entire counties. Therefore, smart meters and concentrators form a large scale wireless network, in which the concentrators maintain the network.
in such a large scale wireless network, data packets have to be relayed from a source node (source) to a destination node (destination) by multiple hop communications unless the source and the destination node are one-hop neighbors. Therefore, optimal routing of the packets is of primary importance, because the network requires high reliability and low latency for both metering information and control packet transmission.
Before any packet is broadcasted, the smart meter network must be formed. To form the network, all nodes must operate on the same frequency channel. However, most of the wireless technologies, such as IEEE 802.15.4, support multiple frequency channels. This means that nodes are not necessarily configured to operate on the same channel. Therefore, a channel scan process must be first performed before network formation. For example, in the 802.15.4 network, all devices scan for the channel on which a personal area network (PAN) coordinator operates.
2. Channel Scan
There are typically two types of channel scan methods, namely, active scan and passive scan.
In active scan, a scanning node broadcasts a scan packet on a channel and then waits to receive a scan response packet on that channel. If no scan response packet is received within a pre-defined period of time, the scanning node switches to another channel and continues the scan process.
In passive scan, the scanning node does not broadcast any packet. Instead, the node only detects a packet containing channel information on a channel. If no desired packet is received within a pre-defined period of time, the node changes to another channel and continues the scan process.
In both active scan and passive scan, the node that manages the network can broadcast channel information packet periodically, or on a need basis. The network management node can also broadcast the scan response packet upon receiving the channel scan packet.
3. Conventional Scanning
A wireless standard can define the channel scan methods. For example, Networks according to the IEEE 802.15.4 standard specify four types of channel scans including passive scan and active scan. However, the conventional channel scan methods are designed for prior single hop networks, in which all nodes can receive from network manager and no channel scan relay is needed. Therefore, known channel scan methods are not suited for multi-hop wireless networks such as smart meter networks. With conventional channel scan methods, a node can never receive the channel information packet if the node is not in the transmission range of the network management node. A non-network management node does not relay the channel scan related packet and does not respond to the channel scan packet.
A passive scanning node can miss channel information packet due to channel switching if the waiting time is too short. Missing the packet can cause unpredictable channel scan delay. With a longer waiting time, the scanning node requires a longer time on each channel and therefore, the channel scan process may take more time.
Active channel scan packets can cause significant interference at network startup time when all nodes start broadcasting scan packet, especially in large scale wireless networks such as smart meter networks, which can include thousands of nodes. The interference can also cause unpredictable channel scan delay.
A channel scan process can be performed at network startup time or during normal network operation. Performing fast and reliable channel scan process that minimizes network startup time for large scale multi-hop smart meter networks is very important.
Unlike conventional sensor nodes that are powered by battery, smart meter nodes are typically powered by electricity from the power system. After each power loss, smart meter nodes may need to re-scan for channel because in the smart meter network, the old stored channel information may not be useful.
For example, at startup time, the node that manages the smart meter network can select a different operation channel. Besides startup channel scan, a fast channel scan process during normal network operation is also important for smart meter networks because channel scan packets can interfere with and delay the data packet transmission. Smart meter networks require reliable data packet delivery with low latency. This indicates that the channel scan process during normal network operation must also be performed efficiently.
Therefore, it is desirable to provide fast and reliable channel scanning for large scale multi-hop smart meter networks.